JPH6-82478A describes a conventional rotational sensor. The conventional rotational sensor will be explained with reference to FIG. 5. Generally, for example, a rotational sensor is provided so as to face a rotor 1 rotating with a wheel of a vehicle. When the rotor 1 of a magnetic body rotates, magnetic flux density passing a Hall IC 2 (detection element) changes because of protruding portions and recessed portions of a gear of the rotor 1. These changes of magnetic flux density are detected by the Hall IC 2. Thus, a rotational speed of the rotor 1 is detected, and the rotational sensor functions as a vehicle speed sensor.
In the rotational sensor, a holder 3 of a cylindrical shape is formed into a single member with a terminal 4 by means of resin molding. One end 4a of the terminal 4 penetrating the holder 3 is electrically connected to the Hall IC 2 through a terminal 6 provided at a base plate 5. In addition, the other end 4b of the terminal 4 penetrating the holder 3 is electrically connected to a core wire of a cable 7. Then, after the holder 3 is fitted into a case 8 of a cylindrical shape, a seal member 9 of a cap shape is formed by means of resin molding, and the case 8 and the holder 3 are tightly sealed so as to inhibit infiltration of liquid. In this case, also the terminal 4 and the cable 7 connected to the terminal 4 are formed into a single member by means of molding. In other words, the terminal 4 electrically connected to the Hall IC 2 is embedded in the holder 3 and the seal member 9.
In the rotational sensor described above, the case 8 and the holder 3 are sealed by the seal member 9. In addition, the terminal 4 is embedded in the holder 3 and the seal member 9. Thus, part where the Hall IC 2 is provided can be tightly covered.
However, because of differences between materials, there exist differences between a coefficient of thermal expansion of the holder 3 and that of the terminal 4, and between that of the seal member 9 and that of the terminal 4. Accordingly, when the rotational sensor is utilized in periodic temperature condition in which surrounding temperature repeatedly rises and declines, though depending on differences in levels of expansion and contraction, there is a danger of forming a gap between the holder 3 and the terminal 4, and between the seal member 9 and the terminal 4.
In this case, there is a danger that moisture, oil, or the like, infiltrated from outside the sensor along a core wire of the cable 7, reach the part where the Hall IC 2 is provided through the gap. Such infiltration of moisture or oil tends to cause electric corrosion or short circuit between terminals of the Hall IC 2, which degrades property of the Hall IC 2, and thereby degrading performance of the rotational sensor.
A need thus exists for a rotational sensor which can ensure performance thereof by firmly inhibiting infiltration of moisture or oil into part where a detection element is provided even when utilized in periodical temperature condition. The present invention has been made in view of the above circumstances and provides such a rotational sensor.